Brassinolide is internationally recognized as an efficient, broad-spectrum and non-toxic plant growth regulator. Its effect is higher than the other five types of plant hormones, so the most active regulator is known as sixth type of plant hormone in the world. Brassinolide is widely found in angiosperms, gymnosperms, and some lower plants. From the perspective of the distribution in a plant, it exists in the roots, stems, leaves, pollens, pistils, fruits and seeds. For example, pollens of canola contain relatively abundant brassinolide.
Although chemically synthesized brassinolide or analogues thereof, as mentioned in Chinese patent applications CN1217337A, CN1217338A and so on, are pure, yet their long-term effects are usually not as good as those of naturally-extracted brassinolide products due to its single component. The phenomenon was particularly prominent on 28-homobrassinolide which had been widely used in China.
A brassinolide product extracted from a plant (e.g., pollens) or other natural sources (e.g., beeswax) usually contains several types of structural analogues of brassinolide. It's much easier for domestic and foreign users to promote the use of the natural product. However due to its preparation, its quality is difficult to be stable. If it is further purified, the product is not conducive to industrialization due to increased costs, so that people is impeded to further purify a large amount of the product and to research the activities of brassinolide analogues isolated from it. For example, Zhu, W. M., et al (Synthetic Communications, 32(9), 1385-1391) and Suksamararn, A., et al (Tetrahedron, 58, 6033-6037) synthesized a series of compounds, but the compounds are recognized as ecdysteroid analogues from an insect for the use of ecdysteroid.
Through long-term and arduous efforts, the inventor explored a stable process of extracting (purified) brassinolide analogues from a plant. The inventor carefully studied the various extraction solvents in the process. Although the process needs certain extraction steps, yet various isolated purified natural brassinolide analogues can be collected at one time and shares costs of extraction, so that the process is conducive to industrialization. In addition, the isolated natural brassinolide analogues can be applied alone, or be mixed at a certain ratio and then applied, so that the quality of the applied product is stable and easily controlled. On the basis of a large amount of isolated purified natural brassinolide analogues, the inventor surprisingly found that the natural brassinolide analogues had effects on the promotion of growth, resistance to low temperature and salt tolerance of a plant, and under certain conditions, their effects and activities were higher than those of chemically synthesized brassinolide products in prior arts.